1. Field of the Invention
The present invention belongs to the field of electronic technologies and relates to a thin-film resistor operating as a passive element and its manufacturing method, and a wiring substrate with this thin-film resistor built therein. The present invention also relates to a wiring substrate and its manufacturing method, and in particular, to a wiring substrate with a resistor built therein and its manufacturing method.
2. Description of the Prior Art
With the recent increasing demand for smaller-sized mounting substrates, there have been an increasing number of reports on substrates with a resistor built therein. In terms of the structure, resistor built-in substrates are classified into substrates with a chip resistor part built therein, substrates with a thick-film resistor (paste) built therein, and substrates with a thin-film resistor built therein. Chip-resistor-part built-in substrates are limited in size reduction, and thick-film-resistor built-in substrates do not provide an accurate resistance value. Thin-film-resistor built-in substrates are most excellent in size reduction and provide a relatively accurate resistance value.
Japanese Patent Application Laid-Open No. 4-174590 has reported on a resistor used for a thin-film-resistor built-in substrate and comprising a nichrome alloy, tantalum nitride, ITO (Indium Tin Oxide), or metal silicide. With such a thin film, however, in the patterning method, wet etching may degrade the substrate due to the use of a strong acid, while dry etching may disadvantageously increase the time required for the process. In addition, even the wet etching method has difficulties in achieving the selective etching between the resistor and electrodes or wiring depending on the type of the resistor.
Thin titanium nitride films are conventionally used as contact barriers for semiconductor elements, as reported in Japanese Patent Application Laid-Open No. 63-156341. Japanese Patent Application Laid-Open No. 3-276755 reports on a method for manufacturing a semiconductor device that uses TiN as a barrier metal and a resistor in semiconductor elements. This resistor, however, relates to a thin TiN polycrystal film. In addition, J. Vac. Sci. Technol. A5, p.1778 (1987) and Papers Presented at Semiconductor Integrated Circuit Technology Symposium, 28, p.97 (1985) report a smaller and a larger resistance values of the thin TiN polycrystal film, that is, 20 to 25 .mu..OMEGA..multidot.cm and 1,300 .mu..OMEGA..multidot.cm, respectively. In this manner, the thin TiN polycrystal film cannot be easily formed into a thin high-resistance film and has a large temperature coefficient of resistance.
On the other hand, Japanese Patent Application Laid-Open No. 61-148732 reports the use as a heating resistor for a temperature detecting element of an amorphous metal compound that is a metal nitride such as TiN or TaN produced by means of high-frequency magnetron sputtering. Due to the variation of the resistance value caused by the temperature, however, this resistor was not suitable as a typical circuit resistor such as a terminal resistor.
A composite consisting of amorphous and crystal titanium nitride is disclosed as a surface treating layer for stainless steel in Japanese Patent Application Laid-Open No. 3-6362, a coating layer on a hard base substrate in Japanese Patent Application Laid-Open Nos. 5-209120 and 9-209121, a thin non-magnetic film for a magnetic head in Japanese Patent Application Laid-Open No. 3-132006, or a semiconductor contact barrier in Japanese Patent Application Laid-Open No. 4-206818. The manufacturing methods disclosed in these applications inject Ti ions into stainless steel in an atmosphere containing nitrogen, inject univalent boron ions into a titanium nitride coated layer formed on a hard base substrate by means of the arc ion plating method using cathode arc discharge, heat the substrate to 300.degree. C. or more after ion beam sputtering, or inject ions after the formation of a TiN crystal film. In this manner, the process for forming a composite consisting of amorphous and crystal titanium nitride is complicated.
In addition, due to the needs for smaller-sized mounting substrates, there is an increasing demand for substrates such as build-up circuit boards which have a fine wiring of a multilayer wiring structure. Accordingly, there have been an increasing number of reports on substrates with a resistor built therein. In terms of the structure, resistor built-in substrates are classified into substrates with a chip resistor part built therein, substrates with a thick-film resistor paste built therein, and substrates with a thin-film resistor built therein.
Of these substrates, chip-resistor-part built-in substrates are limited in size reduction, and thick-film-resistor paste built-in substrates do not provide an accurate resistance value.
On the other hand, thin-film-resistor built-in substrates are most excellent in size reduction and provide a relatively accurate resistance value. Japanese Patent Application Laid-Open No. 4-174590, Japanese Patent Application Laid-Open No. 6-85100, and Japanese Patent Application Laid-Open No. 7-34510 have each reported on a resistor used for a thin-film-resistor built-in substrate and comprising a nichrome alloy, tantalum nitride, ITO (Indium Tin Oxide), or metal silicide.
In addition, in order to prevent the resistance value from being degraded over time due to the diffusion between the resistor and an electrode or wiring, Japanese Patent Application Laid-Open No. 4-174590 and Japanese Patent Application Laid-Open No. 7-34510 have reported on structures in which a diffusion prevention film is formed in the interface between the resistor and the electrode or wiring and in which the surface of a nickel chrome (nichrome) alloy layer acting as a resistor is passivated.
Furthermore, those electrodes or wires in a build-up circuit board which are manufactured using the photolithography technology are allowed to adhere to the resistor by roughening the substrate, but the roughening of the substrate is not suitable for fine wiring.
A substrate with a fine wiring is produced by a process using sputtering, and in this case, Cr, Ti, Mo, or Zr is generally used as adhering ground coat metal for electrodes or wires. For example, Japanese Patent Application Laid-Open No. 55-158697 reports on a substrate using Ti as a wiring ground coat.